1. Field of the Invention
Embodiments of the present invention generally relate to sensors for monitoring production fluid characteristics in an artificial lift well. More particularly, embodiments relate to a low profile sensor installable on a rotating or recipcocating string in a well rather than on a tubing string.
2. Description of the Related Art
Artificial lift wells depend on pumps or the like to move hydrocarbons, water, or other liquids in a wellbore to the surface. Typically, down hole pumps are used to pump the liquid(s) to the surface. For example, an electric submersible pump (ESP) can be lowered into the wellbore to a depth at which the liquid (e.g., oil) collects. The pump can be powered from the surface by a power conductor (e.g., a conductor cable) that runs to an electric motor located adjacent the pump. As the pump operates, the fluid is urged upwards in a string of production tubing toward the surface where it is collected. Conditions around the pump, like temperature and pressure, can be monitored during production. In wells using ESPs, sensors detecting temperature, pressure, and the like can be mounted on or proximate to the pump located at a lower end of production tubing. Also, the power conductor powering the pump can also provide power to the sensors and can provide a signal path for information from the sensors. ESPs are routinely pulled from wells for maintenance and replacement. The sensors which are mounted on, adjacent to, or proximate to the ESP are also returned to the surface when the ESPs are pulled, providing an opportunity to also inspect, maintain, and/or replace the sensors.
In other applications in which down hole ESPs are not used, placing, powering, and replacing down hole sensors can be more difficult. For example, rod pumps (e.g., progressive cavity pumps) use a rod that extends from the surface to a rotor located down hole in the well. The rod can be rotated from the surface to turn the rotor in a stator down hole to pump the liquids to the surface. The rod pump does not have a down hole source of power for a sensor and the pump itself is smaller than an ESP, making the placement of a sensor difficult. Currently, in applications in which down hole pumps are not used, sensors are placed on production tubing that surrounds the rod string. As a result, replacement of the sensor requires the production tubing to be pulled.
In other examples in which down hole ESPs are not used, a reciprocating pump can include a plunger and valve pump assembly that can be positioned down hole and a beam and crank assembly at the well surface that can create reciprocating motion in a sucker-rod string that connects to the down hole plunger and valve pump assembly. The pump contains a plunger and valve assembly to convert the reciprocating motion of the rod string to vertical fluid movement. As with rod pumps, the reciprocating pump does not have a down hole source of power for a sensor. Again, currently, sensors are placed on production tubing and therefore require the production tubing string to be removed to gain access to the sensor (e.g., to perform maintenance on the sensor or to replace the sensor).
When operating progressive cavity pumps and reciprocating rod pumps, the rods can be pulled to inspect, repair, or replace a damaged pump or rotor. The ability to deploy the sensor on the rods (rather than on surrounding tubing) could prevent a costly heavy workover to remove the tubing. The ability to deploy the sensor on the rods can also provide an inexpensive means of temporary deployment of the sensor for well testing or flow optimization.
What is needed is a more effective and efficient way to monitor wellbore conditions in the area of a down hole pump and a simpler way to remove sensors in the event they need replacement.